1. Field of the Invention
This invention relates to a water-based adhesive and coating agent which is especially useful for the coating and bonding of wood and other porous materials and which also has good pot life.
2. Description of the Art
At present, urea resins, melamine-urea co-condensation resins and phenolic resins are used for the adhesives in the manufacture of plywood. The evolution of formaldehyde from these materials has been found to have adverse environmental effects. This evolution of formaldehyde is difficult if not impossible to avoid in the production of plywood and for this reason substitute adhesives have been sought. Various non-formaldehyde yielding water-based adhesive compositions have been suggested but many of them have inadequate water resistance and/or short pot lives as well as other disadvantages. One such adhesive system has been suggested in U.S. Pat. No. 3,931,088 wherein there is disclosed an adhesive comprising (1) an aqueous solution of polyvinyl alcohol, and (2) a hydrophobic solution of an isocyanate compound in an organic solvent. Such compositions can also contain an anionic surface active agent. In contrast, the adhesive compositions of the present invention require no organic solvent and no polyvinyl alcohol in them.
The Official Digest (Of the Federation of Societies for Paint Technology), February 1960, page 213 et.seq. discloses the formation of "blocked" or heat-latent isocyanates with alcohol and subsequent reaction of these materials with amine bearing resins at about 150.degree. C. to form coatings. No amine-bearing resins are required in our invention.